CO2 and Formate Complexes of Phosphine/Borane Frustrated Lewis Pairs

The reaction of a solution of B(C6F4H)(3) and either iPr(3)P or tBu(3)P with CO2 afforded the species R3P(CO2) B(C6F4H)(3) (R = iPr (1), tBu (2)). In a similar fashion the boranes, RB(C6F5)(2) (R = hexyl, cyclohexyl (Cy), norbornyl), ClB(C6F5)(2), or PhB(C6F5)(2) were combined with tBu(3)P and CO2 to give the species tBu(3)P(CO2)BR(C6F5)(2) (R = hexyl (3), Cy (4), norbornyl (5), Cl (6), Ph (7)). Similarly, the compounds [tBu(3)PH][RBH(C6F5)(2)] (R = hexyl (8), Cy (9), norbornyl (10)) were prepared by reaction of the precursor frustrated Lewis pair (FLP) with H-2. Subsequent reactions of 9 and 10 with CO2 afforded the species [((C6F5)(2)BR)(2)(mu-HCO2)][tBu(3)PH] (R = Cy (11), norbornyl (12)). In related chemistry, combinations of the boranes RB(C6F5)(2) (R = hexyl, Cy, norbornyl) with tBu(3)P treated with an equivalent of formic acid gave [(C6F5)(2)BR(HCO2)][tBu(3)PH] (R = hexyl (13), Cy (14), norbornyl (15)). Subsequent addition of an additional equivalent of borane provides a second synthetic route to 11 and 12. Crystallographic studies of compounds 2-6 and 8-14 are reported and discussed. Further understanding of the FLP complexation and activation of CO2 is provided by computational studies.